The Irgun was a Jewish underground organization, founded in 1931 by a group of Haganah commanders, who left the Haganah in protest against its defense charter. In April 1937, during the Arab riots, the organization split—about half its members returned to the Haganah. The rest formed a new Irgun Zeva'i Le'umi (abbr. Etzel), which was ideologically linked with the Revisionist Movement and accepted the authority of its leader, Vladimir Jabotinsky.

Etzel rejected the “restraint” policy of the Haganah and carried out armed reprisals against Arabs, which were condemned by the Jewish Agency. Many of its members were arrested by the British authorities; one of them, Shlomo Ben Yosef, was hanged for shooting an Arab bus. After the publication of the White Paper in May 1939, Etzel directed its activities against the British Mandatory autorities.

At the outbreak of World War II, the organization declared a truce, which led to a second split (see Lohamei Herut Yisrael). Etzel members joined the British Army's Palestinian units and later the Jewish Brigade.

From 1943 Etzel was headed by Menachem Begin. In February 1944, Etzel declared war against the British administration. It attacked and blew up government offices, military installations and police stations. The Jewish Agency and the Haganah moved against the Etzel in a campaign nicknamed the Sezon. Etzel joined the Jewish Resistance Movement and after its disintegration in August 1946, Etzel continued attacks on British military and government objectives.

In April 1947, four members of the organization were hanged in Acre prison. In May 1947, Etzel broke into the fortress at Acre and freed 41 prisoners. In July 1947, when 3 other Etzel members were executed, the I.Z.L. hanged two British sergeants.

In August 1948, the newly formed Israeli cabinet votee to issue an ultimatum telling the Irgun to join the IDF (thereby losing their own organizational identity) or force would be used against them. The Etzel high command offered to disband the organization and integrate its members into the army of the new Jewish state. Full integration was achieved in September 1948.